Resonator silencer



Feb. 27, 1940.

L. MULLER RESONATOR SILENCER Filed Sept, 26, 1936 faja? WPA/.fiez

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Patented Feb. 27, 1940 PATENT OFFICE RESONATOR Smm Lloyd E. Muller,Flint, Mich., assignor to General Motors Corporation, Detroit. Mich., acorporation of Delaware Application September 25, 1936, Serial No.102,878 12 Claim. (Cl. 181-48) This invention has to do with resonatorsilencers and is concerned with the connections of the resonancechambers thereof to the ducts through which the sound waves which are tobe attenuated travel. f

The invention is based on the discovery that it is advantageous toemployrelatively small orices to connect chambers of resonators whose natural.frequencies are relatively high and relatively large orifices to connectchambers of resonators whose naturalfrequencies are relatively low tothe ducts through which the sound waves which are to be attenuated pass.It may be that orifices graduated in size in accordance with the naturalfrequencies of the resonators 'whose Achambers they connect to the ductswould be rnost satisfactory but I have found that very satisfactoryresults can be obtained if only two different sizes of orifices areused.

For resonators whose natural frequencies are relatively high (i. e.,higher than about 300 or 400 c. p. s.), I have found that oricesequivalent in area to circular orifices about 11;" (onesixteenth of aninch) in diameter are most satisfactory. For resonators whose naturalfrequencies are relatively low (i. e., lower than about 300 or 400 c. p.s.), I have found that oriiices equivalent in area to circular orificesbetween about 1A (one-eighth) and about A (one-quarter), preferablybetween M3 (one-eighth) and 352 (live thirty-seconds), of an inch indiameter are most satisfactory. The difference between the optimum sizesof the orifices for the two typesof resonators may be explained upon thebasis of the characteristics of the resonators which it is desirable toaccentuate and the limitations on the accentuation of thesecharacteristics.

In the case of resonators whose natural frequencies are relatively high,it is desirable to accentuate-broaden the range of response. This may bedone by increasing the acoustical resistance of the orifices whichconnect the chambers of the resonators to the ducts through which thesound waves which are to be attenuated pass. Therefore, in the case ofresonators whose natural frequencies are relatively high, relativelysmall orifices of which 'relatively high acoustical resistance ischaracteristic are employed. The limitation, beside the necessity ofmaintaining satisfactory communication between the chambers of theresonators and the ducts, is the size of the orifice that can beproduced commercially iny the material through which the orifice is tobe made.

In the case of resonators whose natural irequencies are relatively low,the characteristic which it is desirable to accentuate is the eillciencyot, response at the natural frequency or frequencies of the resonators.This may be done by decreasing the acoustical resistance of the orificeswhichwconnect the chambers of the resonators to the ducts through whichthe sound waves which are to be attenuated pass. Therefore, in

lthe .case of resonators whose natural frequencies are relatively low,relatively large orifices of which relatively `low acoustical resistanceis characteristic are employed. There are two limitations on theaccentuation of this characteristic. They are that the sizes of theorifices must not be so great that the gases which flow past them willinterfere considerably with the natural movement of the gases within thechambers or as to reduce the acoustical inertance of the resonators totoo low values.

For a better understanding of my invention, reference is made to theaccompanying drawing and the following specification wherein there isshown and described a resonator silencer in Vwhich the invention isembodied.

In the accompanying drawing:

The two parts of Figure 1 constitute a longitudinal section through aresonator silencer in which my invention is embodied;

Figure 2 is an enlarged fragmentary longitudinal section, taken asindicated by the line 2-2 of Figure 3, through the relatively low freequency section of the center tube of the silencer shown in Figure 1;

Figure 3 is a fragmentary section taken as indicated by the line 3-3 ofFigure 2;

Figure 4 is a fragmentary longitudinal section on approximately the samescale as Figures 2 and 3, taken as indicated by the line lli--4 ofFigure 5, through one of the relatively high frequency sections of thecenter tube of the silencer shown in Figure 1;

Figure 5 is a fragmentary section taken as indicated by the line 5-5 ofFigure 4.

The resonator silencer which is. hown in the drawing includes animperforate cylindrical shell IU over whose ends there are secured headsii and i2. Through the heads ii and I2 extend cen'tral orices which areencircled by outwardly extending collars I3 and it and connected by acenter tube i5 whose ends extend into the collars.

Between portions of the shell Il) and center tube l5 near the head i2extend imperiorate annular partitions I6 and l1. The partitions I6 andI1 are separated from each other lengthwise of the shell and the centertube and with the latter and the head I2 define the chambers Il and I 9of two simple resonators with relatively high natural frequencies.

The portion of the center tube I5 between the head II and the partitionI6 is encircled by an imperforate tubular shell 20. 'I'he shell 20 is oflarger diameter than the center tube and of smaller diameter than thecylindrical shell I0 and is coaxial with both and terminates short ofthe head II and the partition I6. Between portions of the tubular shell20 and the center tube I5 about midway between the ends of the silencerextend three imperforate annular partitions 2|, 22 and 23. Thepartitions 2|, 22 and 23 are separated from each other lengthwise of thetubular shell and the center tube and with the latter define' thechambers 24 and 25 of two simple resonators with relatively high naturalfrequen-l cies and two open-ended annular apertures 26 and 21.

Between portions of the cylindrical shell III and the tubular shell 20somewhat farther from the head than from the head I2 extend annularpartitions 28 and 29 which are separated from each other lengthwise ofthe cylindrical and tubular shells. The partition 29 is imperforate andwith the partition I 6 and the cylindrical andl tubular shells definesthe chamber 3|)v of a resonator with a relatively high naturalfrequency. The partition 28, through which extend one`or more orificesin each of which there is secured a tube 3|, defines with the partition29 and the cylindrical and tubular shells the secondary chamber 32 andwith the head II and the cylindrical and tubular shells the primarychamber 33 of a compound resonator with relatively low naturalfrequencies.

The portions of the center tube I5 which are encircled by the chambersI8, I9, 2.4 and are riddled with orifices 34 aboutv 0.003 (threethousandths) of a square inch in area which connect the chambers to thecenter tube. The portion of the center tube Abetween the partitions I 6and 23 is imperforate from the partition I6 to a point about midwaybetween the ends of the annular aperture 21 but the remainder of it isriddled with orifices 34 of the same size as the orifices 34 mentionedabove. 'I'he aperture between the end of the tubular shell 20 and thepartition I6, the annular aperture 21 and these orices connect thechamber to the center tube.

The portionvof the center tube I5 between the head II and the partition2| is imperforate from the 'head to a point well within the annularaperture 26 but the remainderof it is riddled with orifices 35 about0.015 (fifteen-thousandths) of a square inch in area. The aperturebetween the end of the tubular shell 20 and the head II, the annularaperture 25 and the orifices 35 connect the chamber 33 to the centertube.

As the drawing indicates, the orifices 34 may be formed in pairs bymaking in the material of which the center tube is to be formed pairs ofshort slits which extend lengthwise and are separated circumferentiallyof the tube and pressing the material between each pair of slits out ofthe plane of the material without breaking it away therefrom at the endsof the slits so as to form shields 38 which bridge the' space betweenthe slits from end to end and are elevated above the plane of thematerial. As the drawing also indicates, the orifices 35 may besimilarly formed but to make them larger than the orifices 34 the slitsare made longer andthe shields 31 pressed farther outv of the plane ofthe material from which the center tube is to be made.

'I'he silencer shown in the drawing was designed i'or installation inthe exhaust system of an internal combustion engine with the collar I 3connected to the exhaust pipe and the collar I4 to the tail pipe of theengine so that the exhaust gases of the engine pass through its centertube I5 in the course of their passage to the atmosphere. The resonator32--3I-33-26-35 and the resonators 244-34, 25-34, 30'-21-34,' I8-34 and|1--34 are, of course, so tuned in the manner set forth in the Wilsonapplication Serial No. 470,700, filed July 25, 1930, and thecorresponding foreign patents, vi z., Canadian Patent'No. 348,037,British Patent No. 391,180, French Patent No. '720,611 and ItalianPatent No. 300,037, that they respond to and attenuate by resonance,respectively, sound waves of relatively low frequencies and sound wavesof relatively high frequencies which occurin the exhaust gases of theengine.

I claim:

1. In a, silencer, a tube which is riddled throughout a portion `of itslength with orifices equivalent in area to circular orifices aboutonesixteenth of an inch in diameter and throughout another portion ofits length with orifices equivalent -in area to circular orificesbetween about one-eighth and about five thirty-seconds of an inch indiameter, a shell which encircles and isv equivalent in area to circularorifices between about one-eighth and about one-quarter of an inch indiameter and throughout another portion of its length with smallerorifices, a shell which encircles and is radially spaced from theriddled portion of the tube, heads which with the tube and the shelldefine a compartment which encircles the riddled portion of the tube,and a partition which subdivides the compartment into chambers ofresonators of relatively low frequency and relatively high frequencywhich are connected to the tube by the larger orifices' and the smallerorifices, respectively.-

3. In a silencer, a tube which is riddled throughout a portion of itslength with orifices of relatively small size and throughout anotherportion of its length with orifices of relatively large size, a shellwhich encircles and is radially spaced from the riddled portion of. thetube, heads which with the tube and the shell define a compartment whichencircles the riddled portion of the tube, and a partition whichsubdivides the compartment into chambers of resonators of relativelyhigh frequency and relatively low frequency which are connected to thetube by the smaller orifices and the larger orifices, respectively.

4. In a silencer, a tube which isV riddled throughout Aa portion of itslength with orifices with relatively high acoustical resistance and'throughout another portion of its length with oriencircles the riddledportion of the tube, and a partition which subdivides the compartmentinto chambers of resonators of relatively high frequency and relativelylow frequency which are connected to the tube by the orifices ofrelatively high acoustical resistance and the orifices of relatively lowacoustical resistance, respectively.

5. In a silencer, a tube which is riddled throughout a portion of itslength with relatively small orices and throughout another portion ofits length ywith relatively large orifices, a shell which encircles andis radially spaced from the riddled portion of the tube, heads whichwith the tube and the shell define a compartment which encircles theriddled portion of the tube, and a partition which subdivides thecompartment into chambers of relatively small and relatively large sizewhich are connected to the tube by the smalle er orifices and the largerorifices, respectively.

6. In a silencer, a duct, and means which defines chambers of resonatorswith natural frequencies above and below about 300 or 400 cycles persecond connected to the duct by orifices equivalent in size to circularorifices about onesixteenth of an inch and between about oneeighth andabout five thirty-seconds of an inch in diameter, respectively.

7. In a silencer, a duct, and means which deiines chambers of resonatorsof relatively low frequency and relatively high frequency connected tothe duct by oriiices equivalent in size to a circular orifice betweenabout one-eighth and about one-quarter of an inch in diameter and asmaller orifice, respectively.

8. In a silencer, a duct, and means which denes chambers of resonatorsof relatively high frequency and relatively low frequency connected tothe duct by orifices with relatively high acous tical resistance andrelatively low acoustical resistance, respectively.

9. In a silencer, a duct, and means which defines chambers of resonatorsof relatively high frequency and relatively low frequency connected tothe duct by orifices of relatively small and relatively large size,respectively.

l0. In a silencer, a duct, and means which de fines chambers ofrelatively small and relatively large size connected to the duct byorifices of relatively small and relatively large size, respectively.

ll. In a silencer, c. duct, and means which denes chambers of relativelysmall and relatively large size connected to the duct by orices withrelatively high acoustical resistance and relatively low acousticalresistance, respectively.

12. In a silencer, a tube which is riddled throughout a portion of itslength with oriiices with relatively high acoustical resistance andthroughout another portion o its length with orices with relatively lowacoustical resistance, a shell which encircles and is radially spacedfrom the riddled portion of the tube, heads which with the tube and theshell define a compartment which encircles the riddled portion of thetube,

and a partition which subdivides the compartment into chambers ofrelatively small and r/elatively large size which are connected to thetube by the orifices of relatively high acoustical resistance and theorifices of relatively low acoustical resistance, respectively.

LLOYD E. MULLER.

